A tire with carcass reinforcement, for example radial carcass reinforcement, comprises a tread, two inextensible beads, two sidewalls connecting the beads to the tread and a crown reinforcement, placed circumferentially between the carcass reinforcement and the tread.
The crown and/or carcass reinforcement comprises one or more rubber plies, optionally reinforced by reinforcing elements or reinforcers such as individual metal wires or metal cords originating from the assembly of several individual metal wires. The metal reinforcers are made of steel.
The crown reinforcement generally consists of at least two superposed crown plies, sometimes referred to as “working” plies or “crossed” plies, the generally metal, reinforcing cords of which are placed virtually parallel to one another within a ply but crossed from one ply to the other, that is to say inclined, symmetrically or asymmetrically, with respect to the median circumferential plane, by an angle which is generally between 10° and 45° depending on the type of tire in question. The cross plies may be supplemented by various other auxiliary rubber plies or layers, with widths that may vary as the case may be, and which may or may not contain reinforcers. Mention will be made, by way of example, of simple rubber cushions, plies referred to as “protective” plies responsible for protecting the rest of the crown reinforcement from external attacks or perforations, or else plies referred to as “hooping” plies comprising reinforcers oriented substantially in the circumferential direction (plies referred to as “zero-degree” plies), whether they are radially outer or inner with respect to the cross plies.
However, these metal reinforcers contribute significantly to the weight of the tire which it is desired to lighten as much as possible, by improving, if possible, their mechanical strength.
It is thus recommended to increase the weight content of elements of the steel, for example of carbon, to a level of 0.9%, or even more, which makes it possible to increase the mechanical strength of the wires, and therefore to reduce the diameter and/or the density thereof in the reinforcing plies, and thus to lighten the tire. A tire is obtained that is lightened but that has a relatively modest endurance. This is because the metal reinforcers are more sensitive to fatigue and to corrosion due to the use of a relatively high carbon content by weight.